//
//  NSData+base64.m
//  Vote
//
//  Created by Pro Mac on 13-1-28.
//  Copyright (c) 2013年 __MyCompanyName__. All rights reserved.
//

#import "NSData+WYBase64.h"

static const char encodingTable[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";//设置编码

@implementation NSData (WYBase64)

+ (id) dataWithWYBase64EncodedString:(NSString *)string{
    if (string == nil)
        [NSException raise:NSInvalidArgumentException format:@""];
    if ([string length] == 0)
        return [NSData data];
    static char *decodingTable = NULL;
    if (decodingTable == NULL){
        decodingTable = malloc(256);
        if (decodingTable == NULL)
            return nil;
        memset(decodingTable, CHAR_MAX, 256);
        NSUInteger i;
        for (i = 0; i < 64; i++)
            decodingTable[(short)encodingTable[i]] = i;
    }
    const char *characters = [string cStringUsingEncoding:NSASCIIStringEncoding];
    if (characters == NULL)     //  Not an ASCII string!
        return nil;
    char *bytes = malloc((([string length] + 3) / 4) * 3);
    if (bytes == NULL)
        return nil;
    NSUInteger length = 0;
    NSUInteger i = 0;
    while (YES){
        char buffer[4];
        short bufferLength;
        for (bufferLength = 0; bufferLength < 4; i++){
            if (characters[i] == '\0')
                break;
            if (isspace(characters[i]) || characters[i] == '=')
                continue;
            buffer[bufferLength] = decodingTable[(short)characters[i]];
            //  Illegal character!
            if (buffer[bufferLength++] == CHAR_MAX){
                free(bytes);
                return nil;
            }
        }
        if (bufferLength == 0)
            break;
        //  At least two characters are needed to produce one byte!
        if (bufferLength == 1){
            free(bytes);
            return nil;
        }
        //  Decode the characters in the buffer to bytes.
        bytes[length++] = (buffer[0] << 2) | (buffer[1] >> 4);
        if (bufferLength > 2)
            bytes[length++] = (buffer[1] << 4) | (buffer[2] >> 2);
        if (bufferLength > 3)
            bytes[length++] = (buffer[2] << 6) | buffer[3];
    }
    realloc(bytes, length);
    return [NSData dataWithBytesNoCopy:bytes length:length];
}

//调用base64的方法
- (NSString *) WYBase64Encoding{
    if ([self length] == 0)
        return @"";
    char *characters = malloc((([self length] + 2) / 3) * 4);
    if (characters == NULL)
        return nil;
    NSUInteger length = 0;
    NSUInteger i = 0;
    while (i < [self length]){
        char buffer[3] = {0,0,0};
        short bufferLength = 0;
        while (bufferLength < 3 && i < [self length])
            buffer[bufferLength++] = ((char *)[self bytes])[i++];
        //  Encode the bytes in the buffer to four characters, including padding "=" characters if necessary.
        characters[length++] = encodingTable[(buffer[0] & 0xFC) >> 2];
        characters[length++] = encodingTable[((buffer[0] & 0x03) << 4) | ((buffer[1] & 0xF0) >> 4)];
        if (bufferLength > 1)
            characters[length++] = encodingTable[((buffer[1] & 0x0F) << 2) | ((buffer[2] & 0xC0) >> 6)];
        else characters[length++] = '=';
        if (bufferLength > 2)
            characters[length++] = encodingTable[buffer[2] & 0x3F];
        else characters[length++] = '=';
    }
#if __has_feature(objc_arc)
    return [[NSString alloc] initWithBytesNoCopy:characters length:length encoding:NSASCIIStringEncoding freeWhenDone:YES];
#else
    return [[[NSString alloc] initWithBytesNoCopy:characters length:length encoding:NSASCIIStringEncoding freeWhenDone:YES] autorelease];
#endif
}

@end
